(1) Field of the Invention
The present invention relates to a flexible synthetic resin pipe joint capable of deformation under bending. More particularly, the invention relates to a flexible synthetic resin pipe joint comprising a joint wall capable of flattening deformation under application of external compression, which defines a packing holding annular groove, and a packing contained in said annular groove capable of flattening deformation, said packing having such structure that the packing is capable of deformation in follow-up of the flattening deformation of the annular groove and is stably retained in the annular groove. In this flexible pipe joint, the joint wall and packing are combined so that there can be attained a structural relationship generating a co-operative action complying with external compression causing deformation.
(2) Description of the Prior Art
A pipe joint comprising a pipe inserting spigot and a pipe receiving socket or faucet, which are connected to each other through a packing, is different from fixed joints such as glued joints and mechanical joints insofar as it is allowed to expand or contract in the axial direction. Especially in case of a pipe joint comprising a large-diameter portion 3 leaving a free space from the periphery of the top end of a pipe inserting spigot 2 in the interior portion of the inner face of a pipe receiving socket 1 as shown in FIG. 1, since the pipe inserting spigot 2 is allowed to be deformed in the bending direction as indicated by an imaginary line, and because of this deformability as well as elasticity in the axial direction attained by connection through a packing 4, excellent flexibility is attained in the joint. In this joint, since an external force applied to the joint is absorbed by expansion, contraction and bending of the joint, there can be attained an excellent effect of preventing occurrence of such problems such as braking in the joint. The packing 4 disposed in a joint of this type should be stably maintained at an appropriate position and should have sufficient durability so that the intended water tightness can be effectively exerted irrespectively of expansion, contraction and bending of the joint. Further, it is technically important that at the step of insertion and connection of the pipe inserting spigot 2, the packing 4 should be prevented from coming off or separating from the attachment position. Accordingly, there have heretofore been proposed various improvements to be made on the structure of the packing per se, the packing attaching groove or the like for setting the packing at an appropriate position and increasing the durability of the packing (long-time maintenance of elasticity).
A most basic structure of the socket in the joint of this type is shown in FIG. 2. A packing attaching groove 5 is formed on the inner face of the end portion of a pipe receiving socket 1 to improve the setting property of a packing 4. In this structure, however, it happens that at the insertion and connection step, the top end of a pipe inserting spigot 2 presses the packing 4 and the packing 4 comes off or separates from as shown by chain lines, resulting in reduction or loss of the water tightness. This defect may also take place when the joint is deformed in the direction of expansion and contraction after completion of the connection.
FIG. 3 is a view illustrating an improvement of the structure shown in FIG. 2, in which the shape of the inner face of the packing 4 is changed so as to eliminate this defect. However, no particular improvement over the structure shown in FIG. 2 is attained by the structure shown in FIG. 3. In the examples shown in FIGS. 4 and 5, the shape and structure of the packing 4 as well as the shape of the packing attaching groove 5 are improved and attainment of certain improving effects can be expected. In this instance, a packing supporting portion 5a shallower than the packing attaching groove 5 and a packing anchoring portion 5b' deeper than the packing attaching groove 5 are formed, and materials constituting the packing 4 are changed with the central portion of the cross-section serving as the boundary. Namely, the packing 4 is composed of a hard rubber 4b on the side fitted in the anchoring portion 5b' and is composed of a soft rubber 4a on the side facing the supporting portion 5a', whereby the setting property of the packing 4 and the water tightness-retaining property and durability are improved. However, it has been confirmed that as this packing receives external forces repeatedly on contraction, expansion and bending of the joint, cracks are formed in the boundary region between the soft rubber 4a and the hard rubber 4b, and finally, the soft rubber 4a and hard rubber 4b are separated from each other and the function of the packing is lost.
In the examples illustrated in FIG. 6, a tongue portion 4c is formed on the packing 4 to enhance the water tightness while moderating the insertion resistance. In this instance, molding is difficult because of the complicated shape and configuration of the packing 4, and the tongue piece 4c is readily made brittle by corrosive components and bacteria during transportation of fluids and no satisfactory durability can be obtained.
As will be apparent from the foregoing illustration, there has not yet been developed a satisfactory joint structure in which a packing is prevented from coming off or separating from a predetermined position at the insertion and connection step with the packing being set at an appropriate position after completion of the connection to maintain a high degree of water tightness for a long time and with the elasticity and bendability of the joint being a assuredly maintained. In order to attain this object, it is necessary to further stabilize the sealing function of a soft joint by making such improvements that certain relationships will be established among the structural characteristics of the shape of the packaging attaching groove, the sectional structure of the packing, the hardness of the packing and the chamfer angle of the top end of the pipe inserting spigot.